1. Field of the Invention
The present invention relates to an improvement in an expanding apparatus for expanding an agricultural product such as a tobacco material or food. More particularly, the present invention relates to an expanding apparatus using carbon dioxide as an expanding agent, which can expand the tobacco material or the like continuously and can recycle the expanding agent in the system without discharging it to the outside.
2. Description of the Related Art
Conventionally, when a cigarette is to be manufactured from the tobacco material, i.e., the shredded tobacco leaf, the tissues of the tobacco material are expanded.
To expand the tobacco material, a gaseous or liquid expanding agent, i.e., an organic solvent, carbon dioxide, or the like is liquefied or pressurized to a high pressure, the tobacco material is held in the expanding agent to impregnate the tobacco tissues with the expanding agent, and the tobacco tissues are pressure-decreased and then heated to expand the impregnated expanding agent, thereby expanding the tissues of the tobacco material. When the tobacco material is expanded in this manner, its volume is increased to decrease the amount of tobacco material necessary for manufacturing a cigarette, and to provide a light smoking taste. The tobacco material expanded in this manner is used to manufacture a cigarette directly or by being mixed with a non-expanded tobacco material.
The expanding apparatuses for performing this expanding process are classified into batch type expanding apparatuses and continuous type expanding apparatuses. In a batch type expanding apparatus, a predetermined amount of tobacco material is stored in an impregnating vessel, a high-pressure expanding agent is supplied to the impregnating vessel to impregnate the tobacco material with the expanding agent, and thereafter the tobacco material is removed, thereby expanding the tobacco material. In a continuous type expanding apparatus, the tobacco material is continuously supplied in an impregnating vessel to which a high-pressure expanding agent is supplied to impregnate the tobacco material with the expanding agent, and the tobacco material impregnated with the expanding agent is continuously removed.
Although the former batch type apparatus has a simple structure, its efficiency is low and a large amount of expanding agent is unpreferably lost in the outer air. The latter continuous type apparatus is efficient and can recover and re-utilize the expanding agent without any waste. The continuous type apparatus, however, requires valve units for continuously supplying the tobacco material in the impregnating vessel while increasing the pressure in the impregnating vessel and for removing the tobacco material while decreasing the pressure in the impregnating vessel. Since air is mixed in the impregnating vessel through the valve units to degrade the expanding efficiency, the expanding agent discharged through the valve units must be recovered.
Recently, carbon dioxide which rarely adversely affects the environment has been used as the expanding agent. However, the operation must be performed at a high pressure in order to impregnate carbon dioxide, requiring that the valve units described above have higher performance.
The size of such an expanding apparatus has been increasing so as to increase the amount of carbon dioxide used in it. Accordingly, in order to prevent an adverse influence on the environment and to decrease the carbon dioxide consumption, carbon dioxide recovery must be maximized as much as possible to decrease the amount discharged to the outside and to efficiently remove air mixed in the impregnating vessel.
Carbon dioxide used for expanding the tobacco material is compressed and used again, as described above. However, since compression of carbon dioxide needs energy, further energy conservation is required. Furthermore, since air is mixed in circulating carbon dioxide, a large facility and energy are required to separate the mixed air. Accordingly, the amount of air mixed in circulating carbon dioxide must be decreased as much as possible.
The expanding apparatus can be used not only as an apparatus for expanding the tobacco material as described above but also as an apparatus, used for drying an agricultural product, e.g., a vegetable, which expands the vegetable to manufacture a dry vegetable which can be cooked easily.